PROJECT SUMMARY The major goal of in vivo studies core (Core B) is to provide support to activities undertaken by Research Projects 1-3 and Core C, by carrying out in vivo studies in small and large animal models utilizing the 4 novel HIV envelope based vaccine platforms developed as part of this HIVRAD proposal. In addition to providing samples for analysis, Core B will also perform immunological assays to characterize the immune responses to vaccination and perform and monitor a repetitive low dose rectal challenge with pathogenic SHIV in non- human primates. Animal models in vaccine research play an important role in helping test the efficacy and safety of potential vaccine candidates as no in vitro system exists that can accurately reproduce the cellular and humoral responses that occur in a mammalian system. The in vivo studies Core B will address 3 specific aims. In Aim 1 we will perform iterative immunogenicity studies in inbred mice using prototype vaccines from each of the 4 vaccine platforms (Years 1 and 2). Core B will supply samples to Core C for the analysis of gene expression profiles, and Project 3 for B cell repertoire analysis and test for Env-specific antibodies to help identify potential candidates to move forward for further testing. In Aim 2 we will test optimized vaccines and vaccine regimens in the novel, genetically modified, VelocImmune mouse and in the rabbit model (Year 3). Here we will focus on analyzing the HIV neutralization activity induced by vaccination as well as identify unique gene expression profiles and analyze Env-specific cellular and humoral immune responses in conjunction with RP2. Based on the data generated from inbred mice, VelocImmune mice and rabbit studies, Aim 3 will test our 2 optimal pre-clinical candidates for evaluation in a non-human primate study (Years 4 and 5). The non- human primate model provides the best system to investigate responses to our novel vaccines. Their immune system is remarkably similar to that of humans and is therefore considered a valuable comparative model to test vaccine efficacy and safety. Here we will monitor and supply samples for Env-specific cellular and humoral immune responses (RP2) gene expression profiles (Core C) and Env-specific B cell repertoires (RP3) following vaccination, then conduct a mucosal SHIV challenge experiment to test vaccine efficacy. Core B has considerable experience in performing numerous small and large animal studies. They are more than capable in coordinating and performing all the animal studies outlined in this proposal, in addition to being highly proficient at performing all immunological assays and animal procedures required in this proposal.